Each "stop" alows for exactly twice as much (or half as much if going down) light to hit the image sensor (or film)... this also holds true for aperture and ISO.

For shutter speed, its easy to think about it if you start at a base line of 1 second. If you start at 1 second, the next "stop" will be 2 seconds, the next 4 seconds, then 8 seconds, then 15 (round down).... Or if you go the other way, starting at 1 second the next stop is 1/2 second, then 1/4, then 1/8, then 1/15 (again rounded) etc.

For aperture, its a little less simple... you pretty much just need to memorize it, but using f/1 as a baseline stop, the next stop is f/1.4 which alows twices as much as f/1, then f/2 which alows twice as much as f/1.4, then f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32

Most moden cameras do also have 1/3rd between them... and this is very likely the case for yours.